1. Field of the Invention
The present invention relates to initiating telecommunications connections having packet-based data sessions and, more particularly, to controlling the packet-based data sessions from a legacy device.
2. Description of Related Art
In traditional telephone systems, each telephone is linked by an access channel (landline or wireless) to a local switch. The local switch provides connectivity with the public switched telephone network (PSTN). When a user places a call from one telephone that is served by a local switch to a remote telephone that is served by a remote switch, the user's telephone sends dialed digits to the local switch, and the local switch responsively signals to the remote switch (e.g., with industry standard “ISUP” signals) in an effort to set up the call. The remote switch then rings the remote telephone, and, when a user answers the remote telephone, the remote switch signals back to the local switch, and the local switch connects the call through the PSTN to the remote switch. The users may then communicate with each other.
By analogy, in contemporary packet-switched communication systems, each legacy terminal (e.g., telephone, mobile station, computer or other data-capable device) may be linked by an access channel with a media gateway. A media gateway provides legacy terminals with connectivity over a packet-switched network such as the Internet. A media gateway controller operates in conjunction with media gateways by receiving information about the connection. The media gateway controller uses the information to initiate the data session on the packet switched network. In this scenario, a caller legacy terminal may be capable of sending and receiving traditional PSTN signaling and media signals to and from an originating media gateway. The originating media gateway may communicate data packets (such as IP packets) with a terminating media gateway connected to a callee legacy terminal. The legacy terminals may therefore communicate with each other using a data packet communications session between the media gateways to which they are connected. Such a communications connection is known in the art as a “voice over-IP” or “VoIP” connection.
A legacy terminal may also retrieve data from a data server on a packet-based data network by connecting over the PSTN to a media gateway, which then connects over the data network to the data server. In this manner, legacy terminals such as cell phones or telephones having a display may access data from data servers such as Web-sites on the World Wide Web.
Eventually, in next generation systems, terminals will have the capability of interfacing directly with a packet-based data network. Smart phones, for example, are being developed to connect directly to Ethernet ports to provide voice connections that are entirely communicated on a data network. As the telecommunication industry transitions from legacy systems to next generation systems, carriers are now commonly employing media gateways that allow transport of legacy communications over packet-switched networks to complete VoIP connections. The following describes how a VoIP call between legacy terminals might be created.
A user of a local legacy terminal places a call to a remote legacy terminal by dialing digits that connect it to a local media gateway (“local MG”) controlled by a local media gateway controller (“local MGC”). The local MGC receives the dialed digits from the local terminal and responsively determines which remote media gateway (“remote MG”) and remote media gateway controller (“remote MGC”) serve the station with those dialed digits. The local MGC may then send a Session Initiation Protocol (SIP) “INVITE” message over the packet-switched network to the remote MGC, seeking to set up a packet-based media session over the network between the local and remote media gateways, and seeking to establish connectivity with the remote legacy terminal. A SIP INVITE message normally carries with it a “Session Description Protocol” block that describes the type of session requested (e.g., voice-over-IP, video, etc.) and other information, such as device capabilities, that will assist the two data network endpoints (i.e. the local and remote media gateways) in setting up a mutually acceptable session. The remote MGC would then respond with a SIP “200 OK” having an SDP containing the SIP address of a remote MGC that services the remote legacy terminal.
Alternatively, the local MG may send the SIP INVITE over the data network using the dialed digits to identify the remote legacy terminal as the destination (e.g. “sip:3125551234@carrier.com”). The remote MG or the remote MGC may have a SIP client that services the remote legacy terminal. The SIP client becomes operable upon registering on a SIP server connected to the data network. During registration, the SIP client for the user of the remote legacy terminal would designate a callee identifier consisting of the dialed digits. The SIP server detects the INVITE message by the callee identifier and routes it to the SIP client in the remote gateway. In response, the SIP client sends a SIP “200 OK” message containing an SDP that contains a remote media gateway. The local media gateway would then establish a media session with the remote gateway.
The remote gateway may alert (e.g., ring) the remote legacy terminal prior to responding to the SIP INVITE message. If the remote legacy terminal answers, then the remote gateway sends back the SIP “200 OK” message. If there is no answer, or if the connection cannot be made for whatever reason, the remote gateway may respond with an appropriate SIP error message.
Media gateways and media gateway controllers advantageously permit legacy terminals to communicate over data packet-based networks. This capability is growing with the increasing use of softswitches and soft mobile switching centers (“soft MSC”). Softswitches and soft MSCs are network devices that provide service for PSTN subscribers over traditional circuit-switched connections but that also include media gateways and media gateway controllers. Legacy terminals connect to the media gateway and media gateway controller in a softswitch or a soft MSC in their service area via a subscriber line. The media gateway and media gateway controller then provide data sessions over the data network to enable VoIP connections for the legacy terminals served by the softswitch or soft MSC.
Media gateways and media gateway controllers initiate and conduct the data session over the data network using various communications protocols. The communications protocols provide flexibility in creating the data sessions by allowing endpoints to specify various characteristics regarding aspects of the data session. These characteristics may relate to parameters that affect the quality of service over the data connection, the cost of making the connection and many other features that ultimately affect the user's experience during the VoIP call.
Legacy terminals, however, do not provide users with the capability of using the flexibility provided by the communications protocols because legacy terminals do not typically comply with the protocols used in the data network connection. For example, legacy terminals are not typically SIP-compliant in that they are not capable of sending and receiving SIP messages. User may only initiate PSTN connections and must rely on media gateways and media gateway controllers to configure data sessions using communications protocols. Various features and characteristics of the data sessions that may affect the cost to the user and the user's experience are therefore beyond the user's control.